Remove deprecated methods

[mmktomato]

Since it was announces that some API endpoints will be deleted, I will remove the corresponding methods. https://nulab.com/blog/product-updates/backlog/discontinued-apis-august-2024/

• GET /api/v2/groups -> getGroups
• POST /api/v2/groups -> postGroups
• GET /api/v2/groups/:groupId -> getGroup
• PATCH /api/v2/groups/:groupId -> patchGroup
• DELETE /api/v2/groups/:groupId -> deleteGroup
• GET /api/v2/statuses -> getStatuses
• GET /api/v2/projects/:projectIdOrKey/groups -> getProjectGroupList
• POST /api/v2/projects/:projectIdOrKey/groups -> postProjectGroup
• DELETE /api/v2/projects/:projectIdOrKey/groups -> deleteProjectGroup
• GET /api/v2/groups/:groupId/icon -> getGroupIcon

They have been already marked as deprecated and will be deleted on Aug 25, 2025. This task should be done right after the deletion date.